From cities to vineyards: sex-specific phenotypic differences between habitats in a generalist bird species, the great tit (Parus major).

Abstract

In vertebrates, habitats differ in many biotic and abiotic factors with potential important consequences on fitness. Measuring phenotypic differences between habitats is a relevant approach to assess habitat quality for multiple categories of individuals such as males and females. Morphological traits have, for example, been used to successfully assess the impact of urbanization on birds. Surprisingly, this approach has rarely been used in farmlands, although it could be useful to assess the constraints of agricultural practices (i.e. habitat alteration, pesticides). We investigated the phenotypic differences between three habitats (forest, urban, vineyard) in male and female great tits (Parus major) to assess the constraints that occur in small cities and intensive vineyards, and to test if one sex may be more sensitive than the other to habitat-specific constraints. We measured three traits that integrate environmental constraints (body size, body condition, carotenoid-based plumage colouration). We found that urban great tits are of lower phenotypic quality (size, condition, plumage brightness) than their forest counterparts even when they live in small cities. Despite intensive agricultural practices, we found no difference in body size and plumage colouration between vineyard and forest birds, and vineyard birds were even in better condition than forest ones. We found that the differences in body condition between habitats were more pronounced for females relative to males. This supports the idea that females may be more sensitive to habitat-specific constraints than males. Our study suggests that food availability is probably not limited for this generalist species in vineyards, contrary to cities.